1. Field of the Invention
The invention relates to a liquid crystal display (LCD) backlight inverter. More particularly, the invention relates to an inverter for driving multiple discharge lamps in an LCD display.
2. Description of the Related Art
A liquid crystal display (LCD) monitor generally needs efficient and low profile backlighting arrangement for effective display. The backlighting arrangement is equipped with one or more discharge lamps that provide backlighting to the display. Among currently available discharge lamps, cold cathode fluorescent lamps (CCFLs) provide the highest efficiency for backlighting the display. The narrow diameter CCFL, for example, is widely used in industry.
With the increase of monitor size, multiple lamps are needed for the panel illumination. In developing the backlight inverter for multiple CCFLs, manufacturers usually prefer to use one single inverter instead of two or more in order to reduce cost and circuit complexity. FIG. 1 shows a perspective view of a dual-lamp display. A display housing 10 encloses an LCD panel 20 and two CCFLs LP10, LP12. These two CCFLs LP10 and LP12 are located at opposite sides of the LCD panel 20. Note that capacitors C10, C12 appear with their lamp load LP10 and LP12 in parallel across a transformer T10's secondary winding. The advantages of the parallel structure in FIG. 1 are low cost and clear modularity. To achieve equal illumination, the transformer T10's secondary current output must be split evenly between the C10-LP10 and C12-LP12 branches. However, layout and component matching preclude a perfect current split, so the lamps LP10 and LP12 tend to receive unequal current. This causes illumination imbalance in the lamps. In addition, any change in lamp characteristics (e.g., aging) can cause current imbalance. Such a condition expedites lamp aging and shortens lamp life. Accordingly, what is needed is a backlight inverter for driving multiple discharge lamps that overcomes the problems of the prior art.